A working machine such as a hydraulic excavator is provided with an engine, a main pump, and hydraulic cylinders. The main pump is driven by the engine. The hydraulic cylinders such as a boom cylinder, an arm cylinder, etc. operate due to pressure oil discharged from the maim pump so as to drive work implements such as a boom, an arm, etc. constituting a front working device. Moreover, the hydraulic excavator is provided with directional control valves and operating devices. The directional control valves such as a boom directional control valve, an arm directional control valve etc. control the flow of the pressure oil supplied from the main pump to the hydraulic cylinders. The operating devices such as a boom operating device, an arm operating device, etc. perform switching operation on these directional control valves.
In addition, among hydraulic excavators configured thus, there is a hydraulic excavator provided with a main controller which is capable of controlling the speed of an engine to a normal work speed at which a work implement can perform normal work and which controls the speed of the engine to an idling speed serving as a speed lower than the normal work speed when an operating device has been returned to a neutral position from an operating position. This kind of background-art technique has been disclosed in Patent Literature 1.